1. Field of the Invention
The present invention relates to an information recording medium having a phase-change type recording layer, such as an optical disk which can be used for recording and reproducing an information, and to a method of manufacturing the information recording medium.
2. Description of the Related Art
An optical disk having a recording layer formed of chalcogenide materials has been studied for use as an optical disk of phase-change type for recording and reproducing an information (hereinafter referred to simply as a phase-change type optical disk). For example, the publication, Material for a rewritable optical disk, H. Okuda, (issued by Kabushiki Kaisha Kogyo Chosakai, May 20, 1989, first edition) describes in detail a technical discussion on the conventional phase-change type optical disk. According to the conventional phase-change type optical disk, the recording and reproducing of information are performed by making use of a phase change between the crystalline state and the amorphous state of a chalcogenide recording layer. The mechanism of recording and reproducing information is performed as follows.
(1) Since the recording layer formed by means of sputtering or vapor evaporation is amorphous, the recording layer is further subjected to thermal annealing treatment or light beam irradiation thereby changing the amorphous recording layer into a crystalline recording layer, which is generally referred to as initialization (crystallization).
(2) A recording pulse of short wavelength and low power is irradiated to a portion of the crystalline recording layer to partially melt the portion which is then quenched to be amorphized forming an amorphous recording mark.
(3) An erasing pulse of long wavelength and low power is irradiated to the amorphous recording mark to crystallize and erase the amorphous recording mark.
A method of overwriting by superimposing an erasing pulse on a recording pulse is also studied now.
As for the multi-layer structure of the phase-change type optical disk, a structure having a dielectric protective layer, a phase-change recording layer, another dielectric protective layer and a metallic or alloyed reflective layer stacked in the mentioned order on an optical disk substrate is generally employed.
A multi-layer structure having a metallic layer interposed between an optical disk substrate and a phase-change recording layer has been suggested in Jpn. Pat. Appln. KOKAI Publication Nos. 62-226446 and 4-265541. Specifically, Jpn. Pat. Appln. KOKAI Publication No. 62-226446 discloses a multi-layer structure wherein a translucent metallic film is interposed as a light absorption layer between an optical disk substrate and a phase-change recording layer for improving the recording sensitivity of the phase transition recording layer. Jpn. Pat. Appln. KOKAI Publication No. 4-265541 discloses a multi-layer structure wherein a metallic film is interposed between an optical disk substrate and a phase-change recording layer for improving the reflectance of the optical disk.
In the multi-layered structure of the conventional phase-change type optical disk consisting generally of a dielectric protecting layer, a phase-change recording layer, another dielectric layer, a light-reflective layer made of a metal or alloy and an ultra-violet curing resin film stacked in the mentioned order, the light absorption of the recording layer becomes higher when the recording layer is in an amorphous state as compared with when the recording layer is in a crystalline state, so that a recording mark distortion is more likely to be caused especially when an information is recorded in high density.